Multimedia and group communications have become an important aspect of telecommunications, and the demand for such continues to increase. For instance, the Final Report of the Public Safety Wireless Advisory Committee to the Federal Communications Committee (FCC), dated 1996, expressed the critical need for communication resources for multimedia. Subsequently in 1998, the FCC established a band plan for the 764 MHz frequencies that included spectrum set aside for public safety wideband. In addition, the Internet Engineering Task Force (IETF) has developed a suite of protocols that are designed for use in multimedia communications.
Since its approval in early 1999 as an official standard, a Session Initiation Protocol (SIP) has gained tremendous market acceptance for signaling communications services on the Internet. As such, numerous products incorporate the SIP standard, including but not limited to SIP desktop telephones, SIP telephony servers, and personal computing (PC) devices running SIP applications. SIP is a text-based signaling transactional protocol, similar to Hypertext Transfer Protocol (HTTP) and Simple Mail Transfer Protocol (SMTP), and works in the Application layer of the Open Systems Interconnection (OSI) communications model. SIP messages are used for call control, e.g., to control interactive communications sessions or calls, such as voice, video, and chat, between users in a communications network. Each user is typically associated with a wireless communication device that is connected to the network.
SIP was designed for controlling media communication sessions and for establishing media communication sessions between an initiating device and one recipient device or a group of recipient devices. Moreover, for communications between a group of devices, there are typically limited shared radio resources for transmitting and receiving media data. Therefore, communication systems may accordingly implement some form of floor control to control access to those limited shared radio resources.
For many decades, half duplex two way radio networks have provided reliable and convenient communications using limited shared radio resources. For example, “walkie-talkie” and citizens band (CB) radio networks have enabled users to maintain direct communication channels with other users over extended periods of time. The push-to-talk (PTT) and “instant on” features of half duplex radio devices provide desirable modes of wireless communication for users such as truckers, construction and industrial site personnel, military personnel, taxi dispatchers, police and fire personnel and numerous others. Modern communications systems designed for public safety still typically allocate only one logical media stream in a network, which is shared among network participants. A floor control mechanism then dictates which device in the network is permitted to send media at a given time on a given stream.
Push-to-talk over cellular (PoC) is a recent technology that enables familiar PTT and “instant on” features of conventional half duplex radios, but using mobile communication devices operating over modern cellular telecommunications networks. Using PoC, wireless communication devices such as mobile telephones and notebook computers can therefore function as PTT half-duplex radio devices. Other types of multimedia call models (MMCMs) are also available that provide functionality similar to PoC.
Floor control in a PoC or MMCM session is generally maintained by a PoC or MMCM network server that controls communications between two or more wireless communication devices. When a user of one of the communication devices keys a PTT button, a request for permission to speak in the PoC or MMCM session is transmitted from the user's device to the PoC or MMCM server using, for example, a real-time transport protocol (RTP) message. If no other users are currently speaking in the PoC or MMCM session, an acceptance message is transmitted back to the user's device and the user can then speak into a microphone of the device. Using standard compression/decompression (codec) techniques, the user's voice is digitized and transmitted using discrete voice data packets, such as according to RTP and internet protocols (IP), to the PoC or MMCM server. The PoC or MMCM server then transmits the voice data packets to other users of the PoC or MMCM session, using for example a point to multipoint communication technique.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.